Voice Over Internet Protocol (VoIP) or Internet Protocol (IP) Telephony is a technology that allows a user to make a telephone call over the Internet or a dedicated network in IP packets, instead of over dedicated voice transmission lines.
With a VoIP service, it is possible for a user to move their VoIP phone to virtually any IP network and have the ability to make and receive calls at their home phone number, which is commonly referred to as a personal telephone number (TN). This is, in fact, one of the benefits of VoIP service, whereby for example a user can take their VoIP phone with them to a hotel with broadband Internet service and have their home phone ring in their hotel room. By contrast, traditional telephone service is tied to a specific location by nature of the circuit-based telephone network.
The problem with this new capability of VoIP, however, is that the traditional approach utilized by emergency services personnel to locate an individual in the event of an emergency 911 call no longer works reliably in VoIP systems. For example, a VoIP customer's location is recorded as their billing address and all calls originating from the customer's VoIP phone are assumed to be originating from the home address of the customer. If the customer takes the VoIP phone to a second location, such as a shore vacation home for the weekend, and a life-threatening medical emergency prompts the customer to dial 911, then the 911 call would be routed to the Public Safety Answering Point (PSAP) in the area of the customer's billing address, not their current address at the shore vacation residence.
Some VoIP service providers have attempted to solve this by routing 911 calls on their VoIP network to an intermediate dispatch center that determines which PSAP to route the call to. The intermediate dispatch center includes an operator for answering the emergency 911 call. The operator interrogates the caller to determine their location and then routes the call to the PSAP in the location of the caller. However, this approach can add extra time to the emergency response that can be critical to safety. Moreover, it is a labor intensive and relatively expensive for the service provider to maintain.